Slavsk (Russian: Славск; German: Heinrichswalde; Lithuanian: Gastos[7]) is a town and the administrative center of Slavsky District in the Kaliningrad Oblast, Russia, located 105 kilometers (65 mi) northeast of Kaliningrad.

[2] In 1454, King Casimir IV Jagiellon incorporated the territory to the Kingdom of Poland upon the request of the anti-Teutonic Prussian Confederation.

[10] After the subsequent Thirteen Years' War (1454–1466), it became a part of Poland as a fief held by the Teutonic Knights,[11] and by Ducal Prussia afterwards.

From 1701, it formed part of the Kingdom of Prussia, and in 1819 it became seat of the Prussian Elchniederung district.

[7] According to German data 16,000 Lithuanians lived in the district in 1890[12] (29% of the population).